Practice Questions Answers

Original Document which includes notes and a slide presentation on Linkage Groups and Chromosome Maps located at:

http://www.biologycorner.com/APbiology/inheritance/12-2_gene_linkage.html

1. A dumpy winged (dd) fruit fly with long aristae (AA) is crossed with a long winged (Dd) short aristae (aa). Show the cross and the phenotypic proportions.

50% will be Long winged, Long Aristae / 50% will be dumpy winged, long aristae

2. A fruit fly with short legs (ll) and vestigial wings (gg) is crossed with one that is heterozygous for both traits. Assuming the dominant alleles are on separate chromosomes, show the cross and the expected phenotypic proportions.

50% will be long legged, vestigial wings / 50% will be short legged, normal wings

3. In fruit flies, red eyes is a dominant allele located on the X chromosome. The recessive condition results in white eyes. The tan body trait is also X-linked and is dominant to yellow bodies. A female who is heterozygous both traits with the dominant alleles located on the same chromosomes (cis ) is crossed with a white eyed, yellow bodied male. Show the cross and the phenotypic proportions (Don't forget these traits are X-linked!)

 

4.  Chromosome Map Problem  

In pea plants, flower color and pollen shape are located on the same chromosome.    A plant with purple flowers and long pollen (AaBb) is crossed with one that is recessive for both traits (aabb). The results are as follows:    

a) Are the chromosomes of the AaBb parent in the cis or trans position? Sketch a punnett square showing the expected offspring.

Since the majority of the offspring are like the parents, not recombinants, then you would assume that the alleles were in the cis formation. 6% of the time you have a crossing over even that resulting in recombinants.

b) How far apart are the two alleles? 6 map units